I updated to Big Sur and lost my Microsoft Excel. How do I get my excel files back?

Even if your Excel program will no longer operate, your files should still be where they were.

Microsoft does not provide free upgrades between major versions of their Office products (unless you subscribe to Microsoft 365) and older versions of Office are not compatible with macOS Catalina or Big Sur.

If you have a version of Microsoft Office that is not compatible, you can either subscribe to Microsoft 365 or you can make a one-time purchase. See: https://products.office.com/en-us/buy/compare-microsoft-office-products-for-mac?ms.officeurl=mac-compare-redir

Or use the free and very good Libre Office https://www.libreoffice.org/

or the free Microsoft Office on the web: https://products.office.com/en-us/free-office-online-for-the-web

or Google Docs: https://www.google.com/docs/about/

or Apple’s Pages and Numbers

I have MS Excell v. 16.52

Can anyone tell me it will work under Big Sur?

Thanks

Yes -- that is the current version and works under Big Sur. I use that version with Big Sur 11.6 (and earlier Big Sur versions).